Dave at Wheel Enhancement was very helpful to me....

I need new tires on my 2009 C2S.... Background: I love Michelins but have an open mind (beer did that to me).

Question 1: Michelin Pilot PS2 (N Rated) vs Super Sports?

The SSs are cheaper (about $500 less total for four 19" ) and get way more mileage (300 vs 220 rating). The web research I did reveals the SSs are a better tire in all categories including grip street and track... therefore a no brainer for me as I am not committed to the big "N". Any experience or opinions about this? I am a bit skeptical as there is no free lunch although technology can advance (for the rears: tread depth for the SSs is 10/32 PS2 8.5/32 so may explain the mileage difference.... odd the front tire size had different depths).

Question 2: Wheels sizes?

I am considering moving from 19" rims to 18"s. 19" are standard on the "S" while 18" standard on the "base". My manual denotes either are fine and web research denotes that those tracking my model use 18" to save money. I am considering moving to 18" to both save some money on tires, but I feel the ride is just stupid on certain bump types and I believe this move to rubber bands over rims is just poser lipstick. Any comments or opinions regarding my desire to move to smaller rims? Regarding aesthetics, it appears that the tire dimensions compensate for wheel well fill. 18 compare 19 Front: 235/40 vs 235/35 Rear: 265/40 vs 295/30. Opinions?

Question 3: Offsets and spacers?

Tough to find folks who really understand this one. The front wheel widths and offsets are the same 18" and 19". But the rears are different. The rear 19" rim is .5" wider and the offset is 7mm more than the 18" wheels. If I get this correctly, the rears stick out 20mm wider with the 19" and therefore 18" will look less aggressive... a differentiator between the S and base models. So.... do use spacers? I know Porsche sells 5mm spacers for this car but I got to go 20mm for the same look and this makes me very uncomfortable. Am I getting this correctly? Opinions?

Bonus Question 4: Custom wheels?

Another issue with Q3 above... just kicking this around.... comments appreciated if you have experience... I was thinking if I move to 18" wheels, get some gun metal aftermarket wheels that are built with all of this offset stuff already considered. I contacted... I think it was HRE (popular with Porsche folks)... a while ago and they implied they build wheels to order and make anything "work" although they didn't clarify. I didn't want to push as I was not ready to buy at that time. So... bonus points if you have some experience with this one.

A cool resource for wheel and spacer stuff: [www.willtheyfit.com]

PS: I think I will try posting this on a 911 forum.. Compliment to Pedro and the readers here... I find the technical advice here more consistent than the other boards.

Peace
Bruce in Philly

1. SSs >>> PS2s but are slightly more abrupt at break-away. Several of our track guys have used them. SS chunk in heavy AutoX. Otherwise, superb.

If they exist in your size consider BFG g-force2, Much cheaper, made by Michelin, excellent.

2. 18 v 19. I'd go 18. Lighter, cheaper, more durable, ride better, adn fro grip - pay attention to #1

3. They kept offset the same int he front likely toavoid messing with steering geometry. In the rear there is no such thing, so its just a matter of fitment, clearance, adn mechanical stress. A 5mm spacer is probabyl OK if it is fitted, hub-centric, clean adn you use proper bolts (5mm longer). It will place more strain/torque on your wheel bearing and hub however.

Math check:
If the rear tire is 0.5" wider, that's 0.25 (6mm) on both sides. Then move the centerlibne out 7mm due to offset and you are at 6+7=13mm or 1/2".

4. I really like OZ forged light wheels if they can get you the right offset, and you dont mind spending the dough.

I, on the other hand, buy used factory 17" take-offs.

Grant

ps: call me if you want

Grant

gee-lenahan-at-gee-mail-dot-com

1) I would go with the SS tires and not sweat the N spec .

2) I'm using 18" 987 rims for track tires for the reasons you mentioned--no issues to date.

3) regarding the rear offset--just to be clear--what are the offsets on the 19 and 18" wheels?

4) Grant is right that the wider wheel moves the inside of the wheel roughly 6mm closer to something it might contact; you might want to eye ball the struts or whatever else comes closest to the wheel and see what kind of current clearance you have with the 19s.

Quote
MikenOH

3) regarding the rear offset--just to be clear--what are the offsets on the 19 and 18" wheels?

Thanx Grant and Mike... I guess I don't understand offset. Here is all the data:

From 2009 Owner's Manual



Peace
Bruce in Philly

here's what offset is:

Take the rim. Measure across the width of the lips. That's the width.
If a plane were to bisect the wheel, running through the middle of the rim (middle between inside and outside), and you were to have the mounting point (where it bolts to the hub) on that plane, the offset would be zero. In other words half the wheel would be outside the hub mounting point adn half inside.

Offset is the distance, in mm, that the mounting point gets moved INBOARD. So for every mm it moves inboard, the wheel gets pushed out toward and past the fenders by 1mm. If the offset were two feet, the wheel would be cantelevered out past the fenders like an open wheel racer. Positive offset (in much smaller amounts than two feet) is most often done to allow a bigger wheel to not hit the strut.

Now, if you leave the opffset alone, and a wheel is made 1" wider, 1/2 the difference sticks out and the other half sticks in. So it comes 1/2" closer to the strut (maybe hits it) and sticks out 1/2" making the car look more aggressive.

Wht i read is that when porsche specified the rear wheels, it moved the 19" rims out 7mm to avoid contact, because they are 1/2" (12.7mm) wider. That's 6.36mm per side and magically they moved the wheel 7mm.

So it would also be fine to buy a 18" wheel with the same width and offset as the 19.

The did not change the front offset because it affects scrub radius, and that's a bad thing, as i've preached to the point of liekly becoming annoying.

Grant

gee-lenahan-at-gee-mail-dot-com

I snipped this from Will They Fit where I entered 19" and 18" data. Interesting. It looks like an observer will not be able to tell the difference between 18" and 19" versions by looking at how the wheels look on the car. They can tell of course by how "thick" the tire is, but when it comes to filling the wheel well..... well it should look the same with most of the difference being between the wheel and the strut.

Does this match your math? I think you noted the 19" should be 7mm further out but the diagram notes it should be flush (< 1mm Poke?).



Peace,
Bruce in Philly



Edited 2 time(s). Last edit at 07/01/2013 01:50PM by Bruce In Philly (2000 S Boxster, now '09 C2S). (view changes)

Looks like you are good to go, Bruce if I read this correctly.

The 18" wheels will be roughly 6mm farther away from the inside suspension components due to the narrower wheel and another 7mm away due the the offset going from 67mm to 60mm. No spacers needed for clearance since the new wheel will have more clearance room.

With the new tire sizes having a bit larger OD and given the typical Porsche speedos being a bit fast, your indicated speed should be more accurate.

aesthetically, they will not protrude as much. Compared to the 18s, the 19s:

1. are mounted 7mm further out
2, have an additional 1/4" of width from the middle out due to 1/2" total width increase.

This means 6.3mm (1/4") + 7mm = 13.3mm or ~1/2" difference in terms of how well it fills the wheel well.

So in that way my calculations do not agree with theirs. My math is right above for all to see - find my error.

if you hate it, get wheels with 5-7mm greater offset in 18s. No worse than having it factory with 19s.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

I bought a set of 18" 911 wheels for the street when I started running track tires on the OE 17s. He worked out the spacers, longer bolts, etc. and it all came together with no issues. Not cheap, but saved me having to mess around with it.

[www.tirerack.com]

These have just been released and from the early reviews, they have dry traction that approaches Max perf. tires while they can still be driven when temperatures fall below freezing. I didn't see a 265/40/18 size but they do have a 275/40/18 that would be slightly taller.

If they live up to the early billing, I can see going this route mainly because you loose very little in dry/wet traction since they are patterned off the SS and gain a longer driving season since they can handle colder temps. They do weigh a bit more, however.

put on G-force 2s and all was vastly better
(Audi S6)

Grant

Grant

gee-lenahan-at-gee-mail-dot-com